1. Field of Invention
This invention relates generally to controller valves for gas-fired burners which are supplied with a combustible mixture of air and gas, and more particularly to an air-gas controller unit that serves to modulate the volumetric flow rate of the air-gas mixture fed into the burner without, however, altering the ratio between the air and the gas which is preset for optimum combustion efficiency.
2. Status of Prior Art
Among gaseous fuels used in gas-fired burners and furnaces are natural gas and gas derived from coal as well as other petrochemical products. My prior 1984 U.S. Pat. No. 4,432,727 (Fraioli) discloses an infra-red heater in which a flame produced by a gas fired burner impinges on a refractory body that when heated radiates infrared energy to an extent depending on the intensity of the flame. This gas-fired burner is constituted by a cylinder into which is fed the air-gas mixture, the cylinder having a longitudinal slot occupied by corrugated ribbons whereby when the mixture is ignited, a sheet-like flame is emitted from the slot. Similar gas-fired burners are disclosed in the Flynn U.S. Pat. Nos. 3,437,322 and 4,042,317.
In my prior 1984 patent, a pressurized stream of air and gas is fed through separate lines into a mixing control system which includes separately-operated valves, thereby making it possible to control the ratio of air to gas in the mixture supplied to the burner to provide a desired stoichiometric ratio and to maintain this ratio at various valve settings. In this way, one can accurately vary the intensity of the flame produced by the burner and the resultant temperature of the refractory surface of the infrared burner.
Though the invention is of particular advantage in the context of a gas-fired burner which acts as a heat source for an infrared heater, it is by no means limited to this application, for the need exists in all types of gas-fired burners or furnaces for means to maintain a desired ratio of air to gas when adjusting the volumetric flow rate of these constituents to vary the heating temperature produced by the burner or furnace.
For example, should one feed into a gas-fired burner through separate valves a supply of gas and air, these valves may initially be set so that the ratio of air to gas provides complete combustion in the burner. In the case of methane gas, the stoichiometric ratio for complete combustion is 64 grams of oxygen to 16 grams of methane. However, every chemical reaction has its characteristic proportions; hence the ratio for optimum efficiency will depend on the gaseous fuel being used.
But once the desired ratio of air to gas is established by means of separate valves in the air and gas lines leading to the burner, one is then faced with the problem of varying the intensity of the flame without upsetting the desired ratio. Thus if one wishes to increase the intensity of heat yielded by the burner, it is not sufficient to further open the gas control valve, for it is also then necessary to further open the air control valve to provide more combustion air without, however, changing the existing ratio of air to gas. Should an adjustment be made which disturbs the proper ratio, the burner system, though it will supply more or less heat depending on the adjustment, will not then operate efficiently and will waste gas and thereby make the system more expensive to operate.
With prior art arrangements in which an adjustment is made through separately-operated gas and air control valves, it is difficult for an operator to increase or decrease the intensity of the flame without upsetting the desired ratio. This problem is particularly bothersome in commercial installations in which the operator may be lacking in skill and may not be aware that when adjusting the flame he must also be sure that optimum combustion efficiency is being maintained.
My prior 1987 U.S. Pat. No. 4,640,678 (Fraioli) discloses a dual-valve controller having an air-control valve and a gas-control valve, both of which are concurrently adjusted to supply an air-gas combustible mixture to a gas-fired burner. The unique feature of this dual-valve controller is that a single rotary control element acts to effect concurrent adjustment, for when this element is manually turned by an operator, it functions to more or less open both valves to corresponding degrees, thereby adjusting the volumetric flow rate of the air and gas. But in making this adjustment, the air-gas ratio, which is pre-set for optimum combustion efficiency, is not altered.
The practical drawback of my patented dual-valve controller is that it is a relatively complex mechanism, for not only does it require separate air and gas control valves, but also a fairly elaborate cam structure for operating both valves concurrently. As a consequence, this dual-valve controller, though it functions effectively and makes it possible for an operator with a single control element to adjust the volumetric flow rate of the air-gas mixture, is quite expensive to manufacture. The resultant high selling price has discouraged the widespread commercial adoption of the dual-valve controller.